1. Field
One or more aspects of embodiments according to the present invention relate to toll-road collections systems and, more particularly, to a system for providing a tailored illumination pattern for a radio-frequency (RF) automated toll-road collection system.
2. Description of Related Art
Automated toll-road collection systems for motor vehicle traffic may be installed along a road, or at entrances to or exits from a road, on which tolls are charged to vehicles using the road. Such a system may use RF interrogation to read an RF responsive tag in each vehicle passing through a region illuminated with RF radiation, to identify each vehicle and charge a corresponding toll.
In some locations a road on which tolls are to be collected may be adjacent to, for example, a road on which tolls are not to be collected. Unintentional interrogation of the tags in vehicles on the latter may result in tolls being charged when they should not be. Moreover, in some cases a toll-road collection system may fail to collect a toll that is due. For example, a short vehicle, such as an automobile, following a tall vehicle, such as a large truck, may not be adequately illuminated as a result of the short vehicle being in the tall vehicle's shadow.
An RF interrogation system may include a directional RF antenna center-mounted on an overhead gantry illuminating a section of road on which vehicles approaching the gantry are identified by their RF tags. Positioning the RF antenna to one side of the road may mitigate the problem of shadowing but it may exacerbate the problem of illuminating areas in which tolls should not be charged.
Thus, there is a need for an RF interrogation system that illuminates the desired toll collection region and which mitigates vehicle shadowing.